General Overview

In the early game of PvT the Protoss is generally protected by a combination of the Mothership Core and ranged Gateway units. Generally, fast expanding after a Gateway is recommended, since a finished Nexus will be able to defend itself by way of Photon Overcharge, as well as some supplemental units such as Sentries to trap enemies by way of Force Field, and a few Stalkers to kite Marines and Marauders. At this point, you can proxy an Oracle from a Stargate, or Dark Templar to do some economic damage and keep the Terran from spreading out.

The lategame will see the Protoss opt for both of the aforementioned tech choices, with the Terran player responding appropriately with Vikings and Ghosts, respectively. Tempest play is seen as well, with a few Tempests made to snipe Vikings and Medivacs from afar, as well as an Oracle's Revelation being used to watch Medivacs and track drops as well as advancing armies.

Unit Roles and Counters

Zealot: Good against non-upgraded, non-microed Marines and Marauders. Concussive shells slow Zealots down so it is important to use Sentries' force fields to eliminate the mobility of Terran infantry. The Zealot Charge ability in mid-game is important to eliminate Terran ranged advantage.

Stalker: Can be effectively used against Marines in the early game due to superior range and speed, and absorbing hits with their shield which can be regenerated, but this advantage fades when Stim is upgraded. Weak to Marauders. Blink can be used in combination with the Mothership Core or any other flying unit to bypass Terran fortifications and enter the base. Small groups of Stalkers are also used to deny Medivac drops.

Sentry: The Sentry's Guardian Shield ability reduces damage from Marines (33%) and Marauders (20% or 10% vs Stalkers). Force Fields are useful to block chokes and ramps and to split the Terran army. Units trapped by force fields cannot retreat from Zealots. Hallucination is also important, by summoning a Phoenix to quickly scout a base with no expenses incurred if and when it is lost.

Mothership Core: Defends against early Reaper attacks as well as aggression by way of Photon Overcharge. Later in the game it is useful for Blink play, both for getting Stalkers into the Terran base, and for using Time Warp to keep the Terran from microing units efficiently.

Observer: Observers are useful for monitoring enemy army positioning. A well placed observer can show when the opponent unsieges, which is the perfect time to engage. Observers can also be used to spot incoming drops.

Immortal: Strong against Marauders and Siege Tanks due to Hardened Shield and armor damage bonus. Poor against Marines. Large numbers of Stimmed Marauders with focus fire can overcome Immortals. Immortals are also very effective against Thors. Without upgrades and micro, one Immortal can almost kill one Thor.

Colossus: Counters Marine/Marauder bio-balls, but very vulnerable to Vikings.

High Templar: Powerful against Terran bio-balls and sieged Tanks. Templar spells, or lack thereof, often determine the outcome of lategame battles.

Dark Templar: Useful since Terran often do not produce Ravens. Keep them separated and be prepared to run out of the range of scans to keep them alive and waste Terran Orbital Command energy. Dark Templar also force Terran to stay in their base until they either save up scan energy or get a Raven, which can allow you to safely tech or expand.

Archon: Works well in combination with Charge Zealots ("Chargelots"). Archons' high shields can absorb a large amount of damage while the unit does powerful splash damage. However, EMP can allow any Terran composition with ample Ghost numbers to annihilate Archons. In late game situations, Archons' anti-air splash can be useful for killing clumped Vikings quickly.

Phoenix: Counter to Vikings and Medivacs. Good use of Graviton Beam against Siege Tanks can turn the tide of a battle. Can also be used in the place of an Observer to spot (and deal with) incoming drops.

Oracle: Used for early harassment to punish a greedy Terran. A single oracle can kill 5 unstimmed marines, and two can kill 8. Also useful as a general scout, and later can use Revelation to track the movement of the Terran army.

Void Ray: Good counter to Siege Tanks, but vulnerable to Stimmed Marines due to slow movement speed. Can quickly take out a Medivac when charged, so somewhat useful as a drop deterrent if you opened with Stargate.

Tempest: Can be used either as a proxy play to snipe SCVs before Vikings are made in large enough numbers to deal with them, or in late game to shoot Terran air units.

Carrier: Very powerful unit if the Terran lacks armor upgrades. Carriers are weak against Vikings, but only if there are superior numbers of Vikings compared to Carriers. Vikings can be produced faster than Carriers, so make sure you support the Carriers with Stalkers and Sentries. Almost never used in competitive play because of the role overlap with the Colossus.

Protoss Builds vs. Terran

General Openings/Build Orders

Cheeses

Early Game

General information - Pure Gateway armies do well against Terran Bio until they get their upgrades. Zealots tank, Stalkers shoot, and Sentries support. Sentry abilities and good positioning are needed to win engagements when Terran has upgrades. The Mothership Core is also crucial to beating off any early attacks.

General Early Terran Builds

Terran Cheeses

Mid Game

General Information - Now, you transition mainly into one of two splash-dealing units: High Templar/Archon, or Colossus. The latter is generally preferred since the Colossi's BlinkStalker complement can snipe enemy Vikings while the Colossi work on the Marines and Marauders. The huge number of Zealots made during a Chargelot/Templar build is very susceptible to Widow Mines and Hellbats.

General Protoss Compositions

Stalker/Sentry/Colossus

Zealot/High Templar

Zealot/Phoenix/Colossus

Terran Compositions and Responses

MMM + Widow Mines - Some sort of splash damage, whether Colossus or High Templar, is necessary to deal with the large number of Barracks units. Also an Observer or two to spot Widow Mines.

Mech - Immortals and Psionic Storm prove to be very effective here, against Siege Tanks and Hellbats respectively. Archons are also very good at cleaning up Hellbats due to their Biological attribute. Double Robotics Facility plays are effective due to the large number of Immortals needed to deal with Tanks and Thors.

Banshee - 2 Port Banshee builds are uncommon but still well-known, and require either Chrono BoostedPhoenix production if you already have a Stargate, or otherwise a combination of Cannons, Stalkers (with Blink ASAP), and Observers.

Thor-SCV - Normally used for quick all-ins hoping to out-repair any available DPS, although occasionally used for later attacks. Thor builds usually require more Immortals and a lot of focus fire or other way to deal with repairs. Void Rays also take care of them if charged.

In the mid game, be extra careful to place Observers, Pylons or Phoenixes to deny any Medivac drops, especially if you are ahead. This is a common way for the Terran to delay your forces in order to recover.

Late Game

General Information - Late game, you should have both Psionic Storm and Colossus tech at your disposal. Against Bio, be sure to stay on the same amount of bases, or one more, than the opponent. Against Mech, you should be at least a base ahead as Mech play is very defensive but also very economical. Once on four bases, you can begin to add more Warpgates to replenish your army as soon as your supply starts falling, and perhaps transition into air units against a Meching player.

General Protoss Compositions

~5 Tempests (for killing Ghosts and Vikings)

Colossus/High Templar/Archon/Void Ray as damage

Blink Stalkers for attacking Vikings

Zealots for harassment and soaking up damage

Terran Compositions and Responses

MMM + Mine + Ghost + Viking - Positioning is key. As your armies are dancing around each other, keep your Stalkers and Colossus near each other, and Zealots separately so that Zealots don't get in the way of Stalkers chasing Vikings and Stalkers don't get in the way of Zealots charging into the Terran army. Always know where the enemy Vikings are, and position Stalkers in between your Colossus and the Vikings. Keep your Colossus away from cliffs and water where it's more difficult for Stalkers to protect them. When your armies engage, DON'T immediately engage with your Zealots. Wait for the MMM ball to get in range of your Colossus before engaging with Zealots. The Terran wants to kite your Zealots while being out of range of your Colossus, and if you just a-move your Zealots into the Terran and forget about them, the Terran will end up killing all your zealots while avoiding Colossus fire, while your Colossus are dying to Vikings. If Terran runs out of range of your Colossus, PULL your Zealots back and wait for him to get in range of your Colossus again before engaging with Zealots again. Meanwhile, always target fire Vikings with your Stalkers and don't let them just a-move. So in short, when the engagement happens you want to quickly shift-click target a bunch of Vikings with your Stalkers, a-move with the Colossus, and then focus on controlling/dancing your Zealots with the MMM ball. Use Blink to reposition your Stalkers so that they're not in the way of your Zealots and/or so that they're not directly being killed by MMM.

Late Game Ghost-Heavy MMM - You should be Colossus heavy (4-6+ Colossus), and focus on casting Psionic Storm on the Vikings. You'll never get a Storm off the main MMM ball, but it's much easier to get storms off the Vikings and they will actually die pretty quickly (especially if you also have Archons) and then at least you'll still have Colossus against MMM.

Mech - You should already be on two Robotics Facilities and 3 bases. Continue to pump Immortals while adding Stargates and producing Void rays, and take a 4th. Take advantage of the immobility of mech, and use a Warp Prism to spread Gateway units across the Terran bases, denying him or her a 4th wherever possible. Colossi and Psionic Storm are needed to deal with the Hellbats and repairing SCV's, while Immortals and Void Rays can clean up the armored Tanks, Thors, and air units.

Scouting

Early Game

Mid Game

Late Game

Additional Notes

The EMP ability of Terran Ghosts will instantly remove 100 shields from all units in the area of effect, and will temporarily de-cloak Dark Templar. This makes Ghosts a high-priority target.

Raven's Point Defense Drone will absorb 20 attacks from Stalkers. If you have a Stalker-heavy army, Ravens are a high-priority target.

Getting an armor upgrade along with a Sentry guardian shield helps Zealots against Marines; 1 Zealot base armor, +1 for armor upgrade, +2 for shields -- an upgraded Marine attacks for 6 damage -- it takes three times more shots for an unupgraded Marine to kill a Zealot under these circumstances.